The present invention generally relates to an apparatus and a method for operating a sputter chamber equipped with a cover ring and a wafer pedestal and more particularly, relates to an apparatus and a method for self-aligning a cover ring to a wafer pedestal in a sputter chamber.
Physical vapor deposition (PVD) or sputter deposition is a frequently used processing technique in the manufacturing of semiconductor devices that involves the deposition of a metallic layer on the surface of a semiconductor device. The physical vapor deposition technique is more frequently known as a sputtering technique. In more recently developed semiconductor fabrication processes, the sputtering technique is used to deposit metallic layers of tungsten or titanium tungsten as contact layers.
In a sputtering process, inert gas particles such as those of argon or nitrogen, are first ionized in an electric field to produce a gas plasma and then attracted toward a source or a target where the energy of the gas particles physically dislodges, i.e., sputters off, atoms of the metallic or other source material. The sputtering technique is very versatile in that various materials can be deposited utilizing not only RF but also DC power sources.
In a typical sputter chamber, the major components utilized include a stainless steel chamber that is vacuum-tight and is equipped with a helium leak detector, a pump that has the capacity to reduce the chamber pressure to at least 10xe2x88x926 torr or below, various pressure gauges, a sputter source or target, a RF or DC power supply, a wafer holder, a chamber shield and a clamp ring. The sputter source is normally mounted on the roof of the chamber such that it faces a wafer holder positioned in the center of the chamber facing each other. The sputter source utilized can be a W or TiW disc for a process in which W or TiW is sputtered. A typical sputter chamber is that supplied by the Applied Materials, Inc. of Santa Clara, Calif. under the trade name of Endura(copyright) 5500. In some of the sputter chambers, the wafer holder is structured as a pedestal which includes an internal resistive heater.
One of the more important component in the sputter chamber is the clamp ring which serves two purposes during a sputter process. The first purpose is to clamp the wafer to the pedestal heater. The clamp ring holds the wafer in place on the pedestal when a positive gas pressure is applied between the heater and the pedestal such that heat can be efficiently conducted from the heater to the wafer. The second purpose served by the clamp ring is to allow a predetermined flow of argon to leak from under the wafer into the sputter chamber. The clamp ring is generally constructed in a circular shape with an oriented cut-out to match a wafer""s flat contour. A hood is built into the clamp ring and is used for shadowing purpose to protect the lip of the clamp ring from being coated by the sputtered metal particles. The lip portion also allows the force of the clamp ring to be evenly distributed around the wafer.
A cross-sectional view of a typical sputter chamber 10 is shown in FIG. 1. Sputter chamber 10 is constructed by a stainless steel chamber body 12 that is vacuum-tight, a sputter target 16 of W, TiW or Sn, a wafer holder 20 equipped with a heater 22, a wafer lift mechanism 24, a wafer port 28, a pumping port 32, a clamp ring 30 and a chamber shield 34. A DC power supply 25 is connected to a target 21 and a conductive part of the chamber, such as the chamber wall 18 or chamber shield 34, thereby establishing a voltage potential between the grounded chamber wall 18 and the target 21. A DC bias circuit 23 is connected to the clamping ring and thus applies a DC bias to the wafer (not shown). A perspective view of the clamp ring 30 and the chamber shield 34 is shown in FIG. 1A. An enlarged, partial cross-sectional view of the clamp ring 30 and the chamber shield 34 is shown in FIG. 1B. The hood 36 of the clamp ring 30 protects the tip 38 from being coated by the sputtered particles.
As shown in FIG. 1, the chamber shield 34 is another important component in the sputter chamber 10. It forms a seal between the clamp ring 30 and the chamber body 12 such that sputtered particles from the sputter target 16 do not contaminate the chamber wall 18 during a sputtering process. It should be noted that, during the sputtering process, the wafer pedestal 20 is in a raised position with the tip portion 38 of the clamp ring 30 touching the heater 22 on the pedestal 20. In order to achieve a tight seal from the chamber wall 18, a small gap 40 is normally maintained between the clamp ring 30 and the chamber shield 34.
In a typical metal sputtering process where a Ti, W, TiW, Sn or other metal target is used in the sputter chamber, the emission of sputtered particles of the metals is shaped with a forward cosine distribution such that a more desirable deposition process in which metal particles are deposited uniformly at the center and the edge of the wafer can be achieved.
In another typical metal sputtering chamber, instead of the clamp ring 30 shown in FIGS. 1xcx9c1B, a cover ring 42 is used. The cover ring 42, as shown in FIG. 2C, does not clamp onto the surface of wafer 44. The cover ring 42 is equipped with alignment mark shields 46 which extend radially inwardly from an inner periphery 48 of the cover ring 42. The function of the alignment mark shield 46 is to cover the alignment marks (not shown) located on the top surface of the wafer 44 and to prevent the deposition of metal particles thereon. In this configuration, when the wafer lifter 24 raises up with a wafer 44 mounted on top to meet the cover ring 42, the cover ring 42 must be properly seated on the wafer pedestal 20 in order to provide proper shielding of the alignment marks. Such alignment cannot be ensured when the sputter chamber has been operated after a length of time and when the sputter chamber has been cleaned during a preventive maintenance procedure. When the cover ring 42 is not properly seated, or aligned with the wafer pedestal 20, excess metal particle deposition between the cover ring 42 and the chamber shield 34 may cause arcing between the two components. Moreover, metal particles may further penetrate through gaps formed between the two components and deposit on the chamber bottom which may cause serious contamination problem.
It is therefore an object of the present invention to provide an apparatus for self-aligning a cover ring to a wafer pedestal in a sputter chamber that does not have the drawbacks or shortcomings of the conventional apparatus.
It is another object of the present invention to provide an apparatus for self-aligning a cover ring to a wafer pedestal in a sputter chamber such that the alignment marks are properly shielded during sputtering.
It is a further object of the present invention to provide an apparatus for self-aligning a cover ring to a wafer pedestal in a sputter chamber by providing at least two male alignment members on the outer periphery of the wafer pedestal.
It is another further object of the present invention to provide an apparatus for self-aligning a cover ring to a wafer pedestal in a sputter chamber by engaging at least two male alignment members on the wafer pedestal to at least two female alignment member on the cover ring.
It is still another object of the present invention to provide an apparatus for self-aligning a cover ring to a wafer pedestal in a sputter chamber by providing at least two protruding tabs on the wafer pedestal for engaging at least two recessed slots on the cover ring.
It is yet another object of the present invention to provide a method for self-aligning a cover ring to a wafer pedestal in a sputter chamber by engaging at least two male alignment members on the wafer pedestal to at least two female alignment members on the cover ring.
In accordance with the present invention, an apparatus and a method for self-aligning a cover ring to a wafer pedestal in a sputter chamber are provided.
In a preferred embodiment, an apparatus for self-aligning a cover ring to a wafer pedestal in a sputter chamber can be provided which includes a wafer pedestal in the shape of a circular disk equipped on an outer periphery of the disk at least two male alignment members and a cover ring of annular shape that has an inwardly, horizontally extending lip and at least one downwardly, vertically extending lip equipped on an inner periphery at least two female alignment members adapted for receiving the at least two male alignment members when the wafer pedestal is raised to meet the cover ring.
In the apparatus for self-aligning a cover ring in a sputter chamber, the at least two male alignment members may be protruding tabs, while the at least two female alignment members may be recessed slots. The protruding tabs may be L-shaped members with one leg of the xe2x80x9cLxe2x80x9d mechanically fastened to a recess provided in the outer periphery of the circular disk, or one leg of the xe2x80x9cLxe2x80x9d may be fastened to a recess provided in the outer periphery of the circular disk by screw means. The recessed slots are each provided with three tapered surfaces forming a larger opening at the bottom for receiving and guiding the protruding tabs into the recessed slots. The cover ring may further include two downwardly, vertically extending lips with the at least two female alignment members formed on an inner periphery of an inner lip. The wafer pedestal may further include four male alignment members and the cover ring may further include four female alignment members. One of the four male alignment members and a corresponding one of the four female alignment members may have a width that is larger than the other male alignment members and the other female alignment members.
The present invention is further directed to a method for self-aligning a cover ring with a wafer pedestal in a sputter chamber which can be carried out by the operating steps of first providing a wafer pedestal in the shape of a circular disk equipped on an outer periphery of the disk at least two male alignment members; providing a cover ring of annular shape that has an inwardly, horizontally extending lip and at least one downwardly, vertically extending lip equipped on an inner periphery at least two female alignment members adapted for receiving the at least two male alignment members; and raising the wafer pedestal to meet the cover ring until the at least two male alignment members engage the at least two female alignment members.
The method for self-aligning a cover ring with a wafer pedestal in a sputter chamber may further include the step of providing four male alignment members and four corresponding female alignment members. The method may further include a step of mechanically mounting the at least two male alignment members to the outer periphery of the circular disk. The method may further include the step of providing the at least two male alignment members in L-shaped protruding tabs, or the step of mechanically fastening one leg of the L-shaped protruding tab into a recess formed in the outer periphery of the circular disk, or the step of forming the at least two female alignment members in recessed slots. The method may further include the step of forming the recessed slots with three tapered surfaces forming a larger opening at the bottom so as to guide and receive the at least two male alignment members.
The present invention is still further directed to an apparatus for self-aligning a cover ring to a wafer pedestal in a sputter chamber that includes a wafer pedestal in the shape of a circular disk equipped on an outer periphery of the disk at least two protruding tabs, and a cover ring of annular shape that has an inwardly, horizontally extending lip and at least one downwardly, vertically extending lip equipped on an inner periphery at least two recessed slots adapted for receiving the at least two protruding tabs when the wafer pedestal is raised to meet the cover ring.
The apparatus for self-aligning a cover ring to a wafer pedestal in a sputter chamber may further include four protruding tabs on the wafer pedestal and four recessed slots on the cover ring. The at least two protruding tabs may be formed of L-shape with one leg of the xe2x80x9cLxe2x80x9d mechanically fastened to a recess provided in the outer periphery of the circular disk. One of the four protruding tabs and a corresponding one of the four recessed slots may have a width that is larger than the other protruding tabs and the other recessed slots for achieving wafer orientation.